PROTOPLASM AS A PHYSICAL SYSTEM 49 



Whirlpools, candle flames, waterfalls are examples. 

 Such systems also exhibit a constant configuration, and 

 are the seat of special activities, in which access of 

 material and energy from without balances or com- 

 pensates the tendency to disintegration resulting from 

 their own activity and the environmental influences. 

 As with living organisms, their integrity depends upon 

 continual and balanced interchange with the surround- 

 ings. A further general resemblance is that they fre- 

 quently possess permanent features of form and structure 

 which would be impossible as characters of systems in 

 static equilibrium. Such types of equilibria — in which 

 opposed active processes (rather than opposed pressures, 

 tensions, or potentials) have equal and opposite resultant 

 effects, so that the system as a whole retains constant 

 properties — are often called ''dynamic" or ''kinetic" 

 equilibria. The possibilities of complex structure, and 

 of correspondingly complex activity, are at a maximum 

 in systems of this constitution; this is readily seen when 

 we contrast a fountain with still water, or a candle 

 flame or fireworks with their components in static 

 equilibrium. We may say that in such systems the 

 possibilities of the fourth or time dimension are added 

 to those of the three spatial dimensions. 



Living matter, as a system exhibiting a dynamic 

 equilibrium of the special kind^ already indicated, 

 exhibits many characteristic peculiarities, both of 

 structure and activity, which are derived from^ this 

 fundamental feature of its constitution. All living 

 organisms consist largely of structures which would not 

 be possible, as permanencies, if the structural materials 

 were not being continually formed and deposited in such 



